(1) Field of the Invention
The present invention relates to an optical transmitting apparatus, a method of increasing the number of paths of the apparatus, and an optical switch module for increasing the number of paths of the apparatus and, more particularly, to a technique suitable for use in an optical transmitting apparatus having an optical cross connecting function and an optical add-drop function.
(2) Description of Related Art
In a wavelength division multiplex (WDM) optical transmitting system, an optical cross connect function of changing the destination of input light every wavelength of WDM light and an optical add and drop multiplexing (OADM) function of outputting (adding) add signal light having an arbitrary wavelength to an arbitrary path and branching (dropping) and receiving signal light having an arbitrary wavelength from an arbitrary path are in increasing demand.
FIG. 15 is a block diagram showing an example of the configuration of a conventional optical cross connect apparatus (optical transmitting apparatus). An optical cross connect apparatus (hereinbelow, also called a node) 100 shown in FIG. 15 is an optical cross connect apparatus to/from which WDM signal lights having 80 wavelengths (80 channels) λ1 to λ80 at the maximum are input/output for each of four transmission paths #1, #2, #3, and #4 and which can branch (drop)/insert (add) signal lights of 10 wavelengths at the maximum. The optical cross connect apparatus 100 has a plurality of (four) demultiplexers 101 provided for the transmission paths (input transmission paths) #1, #2, #3, and #4, a switch fabric 102 constructed by using a matrix switch (MXS), and a plurality of (four) multiplexers 103 provided for transmission paths (output transmission paths) #1, #2, #3, and #4. In FIG. 15, 200 denotes optical transmitters for 10 wavelengths each for transmitting signal light (add signal lights #1 to #10) to be added to an arbitrary transmission path #i (where i=1 to 4), and 300 denotes optical receivers for 10 wavelengths each for receiving signal light (drop signal lights #1 to #10) dropped from the arbitrary transmission path #i.
Each of the demultiplexers 101 has wavelength selectivity and is provided to demultiplex input WDM light (in which 80 waves of λ1 to λ80 are multiplexed at the maximum per transmission path) by wavelength. The switch fabric 102 is a switch capable of transmitting input signal light which is input to any of input ports to any output port except for an output port of the same transmission path. In FIG. 15, since WDM signal lights having 80 wavelengths λ1 to λ80 are input/output to/from each of the four transmission paths #1 to #4 and signal lights having 10 wavelengths are dropped/added, 330 input ports (=4×80+10) and 330 output ports (total 660 ports) are provided. Each of the multiplexers 103 multiplexes signal lights having 80 wavelengths at the maximum output from each of the output ports of the switch fabric 102 and outputs the resultant light to a corresponding output transmission path #i.
With such a configuration, in the conventional optical cross connect apparatus 100, WDM light input from any input transmission path #i or add signal light #x (where x=any of 1 to 10) output from any of the optical transmitters 200 is input to the switch fabric 102 on the wavelength unit basis via a predetermined input port and the destination (output port) is changed on the wavelength unit basis in the switch fabric 102. The destination is switched to an output transmission path #j (where j is any of 1 to 4 and j≠i) which is different from the input transmission path #i. The signal light after the path has been changed is multiplexed by the multiplexer 103 and output as WDM light to corresponding one of the output transmission paths #1, #2, #3 and #4 or received as dropped signal light #x by any of the optical receivers 300.
In such a manner, the conventional optical cross connect apparatus 100 can switch the path of WDM light which is input from an arbitrary input transmission path #i to an arbitrary output transmission path #i on the wavelength unit basis, and add an add signal light #x to the WDM light to the arbitrary output transmission path #i or drop signal light #x having arbitrary wavelength of the WDM light from an arbitrary input transmission path #i.
Another optical cross connect apparatus is disclosed in, for example, Japanese Patent Application Laid-Open No. H8-237221 (Patent Document 1). The conventional technique of Patent Document 1 is directed to increase flexibility in expansion of the number of input/output highways and the number of input/output links and to facilitate switching of a signal channel. In the conventional technique, as shown in FIG. 1 of Patent Document 1, the apparatus includes: N1 pieces of 1-input M-output optical demultiplexers for separating light signals of N1 series into M signal channels; N1 pieces of M-input (N1+N2)-output optical switches for allocating the signal channels to output destinations (highways) of the N1 series or reception (drop) destinations of N2 series; N2 pieces of M-input N1-output optical switches for allocating signal channels transmitted from an optical signal (add signal light) transmitter to output destinations (highways) of the N1 series; N1 pieces of (N1+N2)-input 1-output optical combiners for combining outputs of the optical switches for each of output destinations of the N1 series; a wavelength converting circuit disposed between the optical signal transmitter and the M-input N1-output optical switches; and N2 pieces of N1-input M-output wavelength selection optical switches for allocating outputs of the M-input (N1+N2)-output optical switches to M receivers (drop destinations) by wavelength selection.
The configuration corresponds to a configuration obtained by constructing the switch fabric 102 shown in FIG. 15 by N1 pieces of M-input (N1+N2)-output optical switches, N2 pieces of M-input N1-output optical switches, N1 pieces of (N1+N2)-input 1-output optical combiners, and N2 pieces of N1-input M-output wavelength selection optical switches.
With the configuration, in the conventional technique, as described in the columns 0023 to 0025, optical signals of the N1 series whose wavelengths are multiplexed are separated into different signal channels and, after that, by using the N1 pieces of M-input (N1+N2)-output optical switches, the signal channels are allocated to the output destinations of the N1 series or the receive (drop) destinations of the N2 series. On the other hand, optical signals of the N2 series to be transmitted (added) are subjected to a wavelength converting process by the wavelength converting circuit every signal channel, and the processed signals are allocated to the output destinations (highways) of the N1 series. The signal channels allocated to the output destinations of the N1 series are combined every destination. At this time, the wavelength of a signal channel to be transmitted (added) can be arbitrarily set, so that the path of the signal channel can be easily switched.
With respect to the signal channels allocated as the receive (drop) destinations of the N2 series from the N1 pieces of M-input (N1+N2)-output optical switches, a signal channel having an arbitrary wavelength on an arbitrary input optical highway can be output to an arbitrary output link without causing wavelength collision by wavelength selection by the N1-input M-output wavelength selection optical switch. Consequently, it becomes unnecessary to consider wavelength dependency in an output link at the time of setting the wavelength of a signal channel.
In such a manner, switch of signal channels between an input and an output (optical cross connect) and switch of a receive (drop) signal channel and a transmit (add) signal channel (OADM) can be simultaneously performed.
The conventional optical cross connect apparatus has, however, the following problems.
(1) Problems on the Number of Ports, Cost, and Size in the Conventional Node Configuration
In the optical cross connect apparatus described with reference to FIG. 15, signal light having a single wavelength is input/output to/from each of input/output ports of the switch fabric 102 (MXS). Therefore, when the number of wavelengths of signal light to be input/output from/to the optical cross connect apparatus increases, the number of input/output ports of the switch fabric 102 becomes very large. Accordingly, the size of the whole apparatus becomes large and the number of optical fiber patch cords to be connected to the switch fabric 102 also becomes enormous. A problem occurs such that it becomes very inconvenient to house and manage the optical fiber patch cords.
Further, to address future increase in the number of input/output transmission paths and drop/add signal light, input/output ports of the maximum predictable wavelengths have to be prepared. Therefore, an enormous switch fabric 102 is necessary from the initial operation. For example, in the configuration shown in FIG. 15, WDM lights having 80 wavelengths at the maximum are input/output to/from each of the four transmission paths #1 to #4 and signal lights of 10 wavelengths are dropped/added. Consequently, each of the number of input/output ports necessary for the switch fabric 102 (MXS) and the number of optical fiber patch cords connected to the switch fabric 102 (MXS) is as enormous as 660. For example, if there is the possibility that one input/output transmission path will be added in the future, 160 input/output ports are necessary as spare ports from the start of use of the apparatus.
The technique of Patent Document 1 has points similar to those points. For example, if the number of input/output wavelengths (M) increases, the number of input/output ports necessary for the optical switches and the optical combiners also increases, so that the apparatus scale and cost increase. In particular, since the number of input/output ports which can be provided for the optical switches and optical combiners is limited in the present techniques, in the case where optical signals of tens of wavelengths are multiplexed per highway, the technique cannot be realized. Moreover, also in the case of addressing future increase in the number of input/output transmission paths and increase in drop/add signal lights, input/output ports of the predictable maximum number of wavelengths have to be prepared for spare (unused) optical switch and optical combiner, so that the apparatus becomes large-scaled and expensive from the initial operation.
(2) Problems on Increase in the Number of Paths (Transmission Paths) in-Service in Conventional Node Configuration
The users strongly demand for in-service upgrading (upgrading which does not interrupt signals being transmitted) from an ROADM node (Reconfigurable OADM node of 2 degrees (where 2 degrees denotes that the number of transmission paths to be handled is two): a node for remotely switching between a transmission signal and drop/add signal light every wavelength) as shown in FIG. 16A to a wavelength cross connect (WXC) node of 3 degrees as shown in FIG. 16B, or from 3 degrees to a WXC node of four or higher degrees as shown in FIG. 16C.
However, in the conventional node configuration shown in FIG. 15, as described above, the number of degrees to be finally requested is predicted, and the switch fabric 102 having the maximum configuration which can deal with signals at the expected number of degrees has to be prepared from the initial operation. For example, as shown in FIG. 17, in the case where a matrix switch 120 of 80 inputs and 80 outputs (80×80) is used and the final number of degrees is expected as four, eight signal lights of one wavelength exists (4 (for transmission signal)+4 (in the case of 100% add-drop)), 10 wavelengths (80÷8) are allocated to one matrix switch 120.
When it is assumed that the number of degrees upon initial introduction is two, 40 input/output ports (=[(2 (transmission signals)+2 (for add/drop signals)]×10 wavelengths) of the matrix switch 120 are used out of 80 input/output ports of one matrix switch 120 but the remaining 40 input/output ports become unused (spare) ports. That is, the same cost as that in the final form is necessary at the initial introduction. Moreover, in the case where upgrading to the number of degrees over expectation is requested, the request cannot be addressed.
The technique of Patent Document 1 also has the same problem. It is necessary to predict the number of degrees finally requested and preliminarily prepare spare optical switches and optical combiners of the maximum configuration capable of handling signals of the predicted number of degrees.